The generational mode uses a 'regulator thread' (RT) to evaluate heuristics while the control thread (CT) is running a cycle. This allows the RT to interrupt an old cycle run by the CT so that the RT can have the CT run a young cycle instead. In some cases, the RT thread's request to cancel old marking may be delayed long enough to land on the young cycle that the RT itself requested. This leaves the collector in a confused state and may result in crashes.